1. Field of Invention
This invention relates to doping semiconductor materials.
2. Description of Related Art
Group III-V semiconductors comprise elements selected from groups III and V of the periodic table. The group III nitride semiconductors, in particular, are used as light emitters for optoelectronic device applications. Group III nitride semiconductors can also be used for high-frequency, high-power, and/or high-temperature electronic devices. These types of semiconductors have the wide bandgap necessary for short-wavelength visible light emission. There are known group III nitride compounds and alloys comprising group III elements, such as Al, Ga and In, and the group V element N. These materials are deposited on substrates to produce layered structures usable in optoelectronic devices, including LEDs and laser diodes. These devices emit visible light over a wide range of wavelengths.
One such group III-V semiconductor is GaN. GaN is a wide-band-gap semiconductor that is used to fabricate blue-light emitting laser diodes. These laser diodes require a region with n-type doping and a region with p-type doping. N-type doping is usually achieved in GaN lasers by introducing Si atoms, which replace Ga atoms and act as donors. P-type doping is usually achieved in GaN lasers by introducing Mg atoms, which occupy the Ga sublattice sites and act as acceptors. An active region is located between the n-type region and the p-type region.
At present, doping levels in semiconductor materials are less than desired for efficient semiconductor device performance. For example, hole concentrations in GaN resulting from p-type doping are usually less than a few times 1018 cmxe2x88x923. Several factors may limit the hole concentration. One factor is the low solubility of the Mg atoms. Another factor is the high binding energy of the holes to the Mg acceptors.
This invention provides doped materials and methods for doping that compensate for local stress caused by dopant atoms having smaller or larger covalent radii than that of the atoms of the sublattice in a group III-V semiconductor material, such as a nitride semiconductor material.
This invention separately provides higher concentrations of dopant in a layer of a group III-V semiconductor material, such as a nitride semiconductor material.
This invention separately provides semiconductor devices having enhanced efficiency.
In various exemplary embodiments, the semiconductor structure according to this invention includes at least one first group III-V layer, such as a group III nitride layer, formed over a substrate. At least a portion of the at least one first group III-V layer is doped by one of an n-type dopant and a p-type dopant. An active layer is formed on or over the at least one first group III-V layer. At least one second group III-V layer is formed on or over the active layer. At least a portion of the at least one second group III-V layer is doped by the other one of the n-type dopant and the p-type dopant. A first electrode is formed on or over the at least one first group III-V layer, and a second electrode is formed on or over the at least one second group III-V layer. The p-type dopant includes a first p-type dopant and one or both of a second p-type dopant and an isovalent impurity. The first p-type dopant has a covalent radius different in size than that of the one of the second p-type dopant and/or the isovalent impurity. The first p-type dopant has a covalent radius that is one of less than or greater than the covalent radius of the base group III element, while the second p-type dopant and/or the isovalent impurity each have a covalent radius that is greater than or less than, respectively, the covalent radius of the base group III element.
The local stress caused by the first p-type dopant is compensated by the local stress caused by the second p-type dopant and/or the isovalent impurity. Because the local stress is reduced, the concentration of the first p-type dopant can be enhanced.
These and other features and advantages of this invention are described in, or are apparent from, the following detailed description of various exemplary embodiments of the systems and methods according to this invention